Ease into interval training. “Build up your intensity intervals slowly, especially for someone who’s deconditioned,” says fitness trainer Sue Grant, supervisor of the active older adult fitness program at the Magdalena Ecke Family YMCA in Encinitas. “Try just one or two higher intensity intervals during each workout at first. As your stamina improves, challenge yourself to (increase) the pace.”

Warm up and cool down. “Make sure you just don’t jump into intense interval training,” Grant says. “To warm up, just do a little mini-version of what you’ll be doing in the hard part of your workout.” To cool down, slowly lower the intensity of activity until you’re breathing normally.

Not every day. Don’t perform interval work on consecutive days. You need to let your body recover and avoid burnout. Every other day or three times a week will produce results with less risk of injury.

Make changes slowly over a period of time. As you become stronger with more endurance, gradually increase the intensity or duration of intervals, but not both at the same time.

Set training goals that are attainable and safe for your physical condition. Although regular interval training will produce results, don’t expect overnight miracles.

Make your intensity intervals an all-out effort. The high-intensity phase should be long and strenuous enough that you’re out of breath, typically one to four minutes of exercise at about

80 percent to 85 percent of your maximum heart rate. Recovery periods should not last long enough for your pulse to return to a resting rate.

Keep it up. The intensity that makes intervals work can’t get easier as you get fitter. You must constantly push yourself and mix in different activities. It doesn’t matter what type of cardio you do — riding a recumbent bike, running stairs or walking at the beach — just keep turning up the intensity over time.

Take precautions. Heart or stroke patients, people who have high blood pressure or anyone over 65 can interval train, but they must do it carefully. “These people need to wear a heart rate monitor, and their physician should give them a maximum exercise heart rate and (the exerciser) needs to stay within that prescribed range,” said Richard Cotton, a Carlsbad exercise physiologist and national director of certification for the American College of Sports Medicine.

— R.J. IGNELZI

Kudos to you. In an effort to boost your health and fitness levels, you diligently walk, run, cycle (pick your cardio activity) for hours each week. But what if you could get the same or better results exercising in just half the time?

Interval training, an exercise regimen that alternates bursts of intense activity with intervals of lighter movement, offers an expedient way to improve cardiovascular fitness, burn optimal calories and keep a workout challenging. Once reserved for fine tuning elite athletes, this type of fitness program now is being used by anyone of any age who wants the most effective workout in the least amount of time.

“People are always saying they don’t have the time to exercise. But, if you only have a half-hour to exercise, do interval training and push yourself into an exercise intensity that you could never do continuously for a long period of time,” says Richard Cotton, a Carlsbad exercise physiologist and national director of certification for the American College of Sports Medicine. “You can get the same health and fitness benefits, maybe more, in a lot less time.”

Interval training shakes up your usual exercise routine and leads to the adaptation response, in which the body adapts to stress by getting stronger. As the body is pushed to new thresholds, it upgrades its oxygen-processing system and begins to build new capillaries to more efficiently take in and deliver oxygen to the working muscles and organs. Muscles develop a higher tolerance to the buildup of lactic acid and the heart muscle is strengthened, all resulting in improved athletic performance.

“So many people take the same walk, jog or bike ride around their neighborhood every morning or night. The body’s fitness level plateaus because it adapts to that level of stress and you stop seeing results,” Cotton says. “When a person does interval training, it mixes it up a bit. They gain more benefits, because they’re stimulating their aerobic system to a higher level than when they just did slower, continuous activity.”

Interval workouts can improve the function and structure of blood vessels, in particular the arteries that deliver blood to the muscles and heart. Along with stronger cardiovascular health comes reduced blood pressure, improved HDL (good) cholesterol levels and a release of stress as endorphins kick in.

In a recent Japanese study, not only did women older than 50 who did walking intervals increase their lung capacity nearly 10 percent but, compared with their evenly paced peers, they also improved knee strength twice as much and lowered blood pressure 2 ½ times as much. Plus, by alternating three minutes of strolling with three minutes of fast, breathless walking, they finished their walks 10 minutes sooner.

Burns more calories.

“In interval training you’re expending more energy in a shorter amount of time. After an intensity workout, it takes longer for your body to recover and cool down, so it will continue to burn more calories,” says Pete McCall, exercise physiologist with the San Diego-based American Council on Exercise (ACE).

“The first 15 to 30 minutes after you finish a hard interval workout is the time to eat that Danish with your coffee. Your metabolism will be elevated to a higher rate then, and your body is burning more efficiently,” he says.

Increases endurance.

In a 2005 study published in the Journal of Applied Physiology, it was found that after just two weeks of interval training, most exercisers doubled their endurance or the amount of time they could ride a bicycle at moderate intensity before exhaustion.

Eliminates exercise boredom.

“Interval training keeps you thinking and makes you pay attention. It keeps exercise interesting, and as long as it’s interesting, you’re more likely to keep it up,” Cotton says.

Lessens delayed-onset muscle soreness.

During intense exercise, muscles produce lactic acid and waste products that can contribute to muscle soreness. But by alternating bursts of intense exercise with easier intervals, you reduce some of the buildup of waste products in the muscles, so exercise is more comfortable.

May reduce repetitive stress injuries.

Performing any exercise for long periods of time can put you at increased risk of overuse problems. Interval training can help prevent injuries often associated with repetitive endurance activities by allowing you to increase your training intensity without overtraining or burnout.

Although formal interval training is often structured around a precise intensity phase with a set period of recovery movement, fitness trainer Sue Grant says there’s no need to be so strict, especially when you first try intervals. This more casual approach to interval training is officially known as fartlek training, Swedish for “speed play.”

“Go ahead and fiddle around with intervals. Use perceived exertion (how hard you believe you’re working) and give it your all-out best effort,” says Grant, supervisor of the active older adult fitness program at the Magdalena Ecke Family YMCA in Encinitas. “But take it at your own (pace) and rest long enough so you can do that next interval blast.”

And, just because you’re pumping up the intensity doesn’t mean you have to give up watching TV while on the elliptical or treadmill. McCall suggests using the commercials as intensity intervals. When your show resumes, watch it and recover.

Interval training can be used to increase the effectiveness of almost any activity.

• Walkers can incorporate short bursts of jogging into their regular brisk walks, or alternate leisurely walking with periods of faster walking. You can alternate two minutes of intensity with two minutes of recovery walking or use outdoor landmarks like light posts or mailboxes to mark intervals.

• Joggers can alternate slow jogs with running, while runners can do intervals of sprints with a slower-paced run. Even swimmers can take the interval plunge and alternate swimming a lap as fast as possible with a slower backstroke lap or one using a kickboard.

• Interval training is a good way to put some zest into your normal gym cardio workout. Instead of zoning out as you pedal for an hour at the same intensity level on a stationary bike, alternate two or three minutes of high resistance with periods of easier work. Treadmill users can push the burn with intervals of steep incline, while elliptical exercisers can maximize their workout by adding bursts of either high resistance or speed.

To really throw your workout a curve, occasionally perform intervals doing new and different activities. Add a jump-rope interval session every week or two, alternating speed jumping with slower paced skipping. Stair climbing can offer some very effective interval training, as you run up long flights of stairs or climb two or three steps at a time and then walk down. The stairs at San Diego County beaches, school stadiums and some tall office buildings are the perfect venue.

“Interval training can increase the workout (benefits) of almost any kind of (cardio exercise) program. It doesn’t have to be painful, but you should be really pushing your comfort zone, pushing to the upper limit of your heart range,” Cotton says. “It’s at that point that you’re getting the most return for your time invested.”